This invention relates to a sewing machine needle and, more particularly, to a needle used for a zigzag sewing machine.
As generally known, a sewing machine needle accompanied by an upper thread is adapted to vertically be reciprocated between an upper dead point and a lower dead point in synchronism with rotation of a horizontal loop taker, so that a thread loop of the upper thread formed beneath a fabric is caught by a hook of the loop taker while the needle ascends from the lower dead point, which thread loop is thereby interlocked with a lower thread to form a stitch. In zigzag stitching operation, the needle is also caused to laterally swing in a predetermined amplitude and, accordingly, while the needle swings laterally there will be a change in the relative position between the needle and the hook of the rotary loop taker in which position the latter is about to catch the thread loop formed about the former. More particularly, as shown in FIG. 1, in a case of the loop taker being rotated in the counterclockwise direction, the thread loop (L) of the needle at the rightmost position is caught by the hook 1 of the loop taker when the needle 2 ascends from the lower dead point by an amount .delta..sub.2, whereas a larger thread loop (L) of the needle 2 at the leftmost position is caught by the hook 1 when the needle 2 goes up from the lower dead point by an amount .delta..sub.1, which is larger than .delta..sub.2. The needle 2 at the leftmost position is therefore subjected to a greater degree of friction with the fabric while it goes up an amount .delta..sub.1, and accordingly the thread loop (L) formed in the leftmost position of the needle 2 will be larger than that in the rightmost position as shown. This may, however, often result in sewing troubles, that is, failure of the hook 1 to catch the thread loop (L). For example, when fabrics 3 of elastic or stretchable nature are being sewn together, the friction between the flexible fabrics 3 and the needle 2 will cause the fabrics 3 to be pulled into a needle hole 4a of a needle plate 4 as the needle 2 descends, while the fabrics 3 are brought up from the needle plate 4 as the needle 2 ascends, as shown in FIGS. 2 and 3 respectively. Such phenomena will prevent the needle thread from being formed into a sufficient loop, especially when the needle 2 is positioned in the rightmost position in the zigzag stitching operation. Whereas, in the leftmost position of the needle 2, when stitching ordinary fabrics 5, a big thread loop (L) will be formed, but the loop (L) has a tendency of inclining to one side and often twisting around the needle 2 as shown in FIG. 4, especially if the thread is made of cotton. Such a thread loop (L) is of course difficult to be caught by the hook 1. Due to the above described sewing problems in which the hook 1 fails to catch the thread loop formed during the zigzag stitching operation, the resulting stitches would include many skipped stitches. However, there has not been found a way to solve this problem.